The collective term CLA is intended to describe a mixture of geometric and positional, conjugated, dienoic isomers derived from linoleic acid, both in the form of free fatty acids (FFAs) and in the form of the respective salts or other derivatives, particularly esters.
CLA is present in nature in the milk and meat of ruminants and is formed as an intermediate compound during the process of biohydrogenation of some polyunsaturated fatty acids contained in their diet, in particular of linoleic acid and of α-linolenic acid. Some of these intermediate compounds escape complete hydrogenation and accumulate in the mammary glands.
The CLA isomer which is predominant in the fatty fraction of ruminant milk is cis-9,trans-11 for which an endogenous synthesis mechanism has also been proposed (Mahfouz et al., 1980, Pollard et al., 1980, Griinari et al., 2000).
Studies carried out within the last three decades have shown this isomer, together with the trans-10,cis-12 isomer, to be involved in many physiological and metabolic functions; this has progressively increased scientific interest in CLA and the biochemical mechanisms in which it is involved.
In particular, the following are indicated, amongst the numerous potential applications of CLA: i) inhibition of carcinogenesis; ii) improvement in immune function; iii) reduction in inflammation; iv) reduction in the catabolic effects of immune stimulation; v) reduction in asthma in animal models; vi) reduction in atherosclerosis (reduction in the LDL (low density lipoprotein) concentration and in the LDL:HDL (high density lipoprotein) ratio); vii) reduction in accumulation of body fat and increase in lean body mass; viii) increased growth in rodent young; ix) reduction in diabetes symptoms in some experimental models; x) reduction in hypertension.
Not all of the physiological effects given above can be attributed to both of the above-mentioned isomers (as is, however, true for the inhibition of mammary carcinogenesis); in some cases, the effect is determined by only one of the two (for example, trans-10,cis-12 is the only isomer which is responsible for reducing body fat mass, whilst the isomer cis-9,trans-11 improves growth and feeding efficiency in rodent young) whereas, in other cases, the effect of the two isomers seems to be a balancing of opposing actions.
In the light of the above-described potential beneficial effects, a need has arisen to increase the availability of CLA both by trying to produce, from ruminants, milk which is richer in that compound, and by trying to provide a CLA-based product for direct administration to human beings, for example, in the form of a food supplement or additive for use in normal food production. In the first case, one of the possible alternatives provides for the supplementing of the animal diet with synthetically produced CLA.
It is also known to synthesize CLA in the laboratory, for example, from vegetable oils such as safflower oil or sunflower oil; the product which is generally obtained is a mixture of isomers of CLA in its various forms such as methyl esters or free fatty acids (FFAs) and can be used in both human and animal food. However, CLA has great disadvantages in terms of stability.
In fact it tends to react very easily with oxygen and other oxidizing agents such as choline hydrochloride or some minerals, particularly in the presence of light or of metals such as copper and iron, degrading rapidly and thus losing its activity. Its poor resistance to oxidation processes renders it particularly unstable and much less easily handled than normal polyunsaturated fatty acids.
CLA must therefore be suitably protected both from the outside environment (during the periods, possibly quite long periods, which elapse between its production and its use) and from the gastric or pre-gastric environment (during use).
Moreover, the high degree of instability of CLA also imposes considerable limitations on the manufacturing processes which lead to its protection; in fact processes in which high temperatures are required for fairly long periods of time would lead to its rapid degradation.
Currently known methods of protecting CLA provide for the use of CLA in the form of calcium salts or in the form of esters, or for the encapsulation of the molecule in a matrix of casein treated with formaldehyde, or even microencapsulation in cyclodextrin.
However, the goal of providing CLA with the characteristics of stability required by the market has not yet been achieved. There is therefore still a need in the sector to have available a CLA-based product the CLA content and, in particular, the resistance to oxidation of which remains substantially unchanged, even over a long period of time of the order of several years, without the need to resort to the use of antioxidants or to storage in an inert atmosphere and which, at the same time, can also remain stable in the gastrointestinal tracts of animals and human beings.